1. Field of the Invention
The invention relates to a method for manufacturing recording heads for data storage devices, and specifically for defining the width of a recording head gap formed in a magnetic recording head.
2. Description of the Related Art
Most recording and reproducing transducers for magnetic storage devices are based on a design incorporating an inductive coil and magnetic core, thus being collectively referred to as "inductive heads." In this design, a magnetic core is surrounded by an inductive coil, which is coupled to electronic circuitry controlling the reading and writing of data to the magnetic storage medium. Magnetic flux is delivered to (or transferred from) the poles of the head core by a magnetic yoke that normally has a greater cross-sectional area than the poles in order to avoid saturation of the yoke region. Data is written on the storage medium in a plurality of data tracks, each having a width based on the medium used to store data. In magnetic storage devices, for example, the track width is limited by the intensity of the media and sensitivity of the recording heads. The general trend in data storage and retrieval technology has been one of decreasing data track width on the storage medium. Consequently, the head gap width, and head core volume are decreased as well, while recording densities and bandwidths have increased. Generally, a single head performs both the recording (write) and reproducing (read) functions, though the optimum writing head gap in a magnetic head is wider than the optimum reading head gap. (For purposes of definition, the gap "length" as used herein defines the distance between the poles, while gap "width" refers to the distance that the length between such poles is maintained.)
The gap in the pole pieces of a recording head is designed to produce a field amplitude capable of magnetically recording data on the storage medium to a sufficient depth, normally considered to be equal to or greater than the reading depth, corresponding to the recorded wavelength. The pole geometry and materials are designed to provide adequate field strength at the signal frequency, along with a rapid decrease of the writing field along the direction of the medium motion, in order to maximize the short-wavelength recording efficiency.
The limits to obtaining high track densities with narrow recording heads are determined by, among other things, the effects of the magnetic fields along the direction of medium motion. These fields can be thought of as fringing fields since they result along the ends of the recording gap as a result of the fringing effect of magnetic fields at the portion of the gap where the flux meets the edges of the core or the gap. As should be readily recognized, these fringe fields can partially erase tracks adjacent to a track being written at a given time, increase the effective read/write width of the head and can pick up the signals from adjacent tracks.
Inductive heads can be used as the basis for a number of recording applications such as video recorders, analog tape recorders, digital tape recorders, and data storage applications, such as tape drives.
Data storage tape drives are widely used in data processing systems as the primary data storage device or, more often, as a back-up data storage device to the system's hard disk drive. Conventional tape drives are designed to transfer data to and from a length of magnetically encoded tape, typically one-quarter inch in width, which is transferred between a supply reel and a take-up reel. While several tape drive designs exist for recording and playing back a data tape, the two most widely used drive technologies up to now have been stationary head tape drives for longitudinal recording and rotary head tape drives for transverse linear or "helical" recording.
In longitudinal recording, a tape drive includes a plurality of adjacent stationary heads which lie across the width of a data tape. In helical recording, one or more heads are provided around the circumferential surface of a rotating cylindrical drum. An advancing data tape encounters the rotating drum such that the longitudinal direction of the tape is angled with respect to the plane in which a recording head on the drum rotates. As such, rotary head helical recording provides a relatively large areal density.
Presently in the tape drive industry, as in other data storage technology areas, there is a movement toward smaller drive dimensions while at the same time increasing data storage capacity. Existing longitudinal and helical recording technologies have proven inadequate in meeting these demands.
Yet another type of recording scheme incorporates an "arcuate scan" of the tape. In arcuate scan drives, a rotating drum having a plurality of heads mounted thereon is positioned perpendicular to the tape and rotated such that each head makes an arcuate path over the tape as the tape passes around the head drum. Arcuate scan recording has been known for some time, but has been disfavored due to the lack of effective servoing schemes for accurately maintaining alignment of the heads with the arcuate data tracks.
U.S. patent application Ser. No. 07/898,926, filed Jun. 12, 1992, now abandoned by J. Lemke (hereafter "the Lemke application"), discloses a relatively compact arcuate scan tape drive for recording and playing back up to approximately 10 gigabytes on a conventional mini-cassette tape, a storage capacity which is higher than that previously obtained with either longitudinal or helical recording. FIGS. 1-3 of the present application are reproductions of FIGS. 1-3 of the Lemke application and constitute a perspective view of the arcuate scan drive, a top view of the head drum/tape interface, and a perspective view of the head drum, respectively. The Lemke application discloses a tape drive including a plurality of heads placed on the front circular face of a rotating drum, with the axis of rotation of the rotating drum being perpendicular to and intersecting with the longitudinal axis of the advancing tape. Head drum 30 rotates about axis 38 to pass heads 35 in arcuate paths along tape 21 as tape 21 passes head drum 30. As the tape advances from the right to the left and the drum rotates in a counterclockwise direction, the heads trace arcuately-shaped data tracks substantially transverse to the longitudinal axis of the tape.
The Lemke application discusses a drum having a plurality of heads which utilizes a sequential three head data transfer and positioning scheme. In the Lemke arrangement, the heads are arranged in triads where the first head is a read head, the second a write head and the third a servo head, each passing over a given track in succession. It should be readily understood that numerous head schemes are suitable for use with arcuate scan disk drives.
Another reason arcuate scan recording has traditionally been disfavored is that conventional head/tape engagement mechanisms employed in arcuate scan tape drives have proven inadequate in maintaining a close contact between the recording heads and the data tape, without simultaneously causing damage to the heads and/or tape in a relatively short period of time. A close head/tape interface is imperative to accurate alignment of the recording heads with the data tracks as well as to obtaining a high storage density on the data tape.
Another significant factor deterring the popularity of arcuate scan technology is the difficulty in manufacturing the recording heads and head drum in a cost effective and precise manner. With the arcuate scan drive disclosed in the Lemke application, for example, a data track width on the order of 0.0005 inch is utilized. The length and width of the recording gap of the read/write head is therefore crucial to accurate performance of the arcuate scan tape drive. The width of the gap is especially critical in defining the track widths which may be utilized in arcuate scan drives since, as discussed above, the width of the gap determines the intensity of fringing fields which may affect adjacent data tracks. Thus, manufacturing ferrite heads having two pole pieces and a recording gap with precisely defined length and width is extremely important in producing a commercially viable arcuate scan drive.
Further, aligning each of the heads on the head drum in a manner which ensures that each head is at the same distance with respect to the rotational axis of the drum is critical to ensuring proper read/write performance. Such alignment must tolerate inaccuracies in manufacturing a number of such heads with such minute gap sizes, imperfections in the heads, head drum, and read/write assembly, and yet be cost effective to maintain the commercial viability of the arcuate scan tape drive.